Debris collection vehicles, such as sewer cleaners, hydro-excavators, and street sweeping vehicles are often provided with an enclosed volume, for example a hopper or collection tank, for retaining collected debris. Generally, a fan is also provided that is configured to draw a vacuum condition within the enclosed volume. In some implementations, the fan is directly driven by an auxiliary engine of the vehicle via a gear box. However, such an approach limits the fan performance by the amount of torque that can be produced by the auxiliary engine. In other implementations, the fan is driven by a fixed displacement hydraulic motor that is driven by a pump. However, this approach can require the motor and the pump to operate at or over their respective maximum rated speeds for successful operation, which can decrease equipment life. Improvements are desired.